Gas turbine engine airfoil frequency design

1. A turbomachine airfoil element comprising:

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 27.5-28.5 inches;

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 13.0-14.0 inches; and

at least two of:

a first mode has a frequency of 34 up to ±10% Hz;

a second mode has a frequency of 92 up to ±10% Hz;

a third mode has a frequency of 178 up to ±10% Hz;

a fourth mode has a frequency of 222 up to ±10% Hz;

a fifth mode has a frequency of 307 up to ±10% Hz; and

a sixth mode has a frequency of 389 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 1EB/1T mode, the third mode is a 1T mode, the fourth mode is a 2EB mode, and the fifth mode includes a 2EB mode, wherein the 1EB and 2EB modes correspond to deflections substantially parallel to the thickness direction, and the 1T mode corresponds to twisting about the radial direction;

wherein the airfoil element is part of a blade;

wherein the airfoil comprises an aluminum-based alloy, the aluminum-based alloy has a density of about 0.103 lb/in 3 , the aluminum-based alloy has a modulus of elasticity of about 10.4 Mpsi at room temperature.

2. The element of claim 1 , wherein three of the first, second, third, fifth and sixth mode frequencies are present.

3. The element of claim 1 , wherein at a minimum cruise speed of 18200-20200 rpm at Mach 0.8 at 35,000 feet:

the first mode has a frequency of 57 up to ±10% Hz;

the second mode has a frequency of 129 up to ±10% Hz;

the third mode has a frequency of 171 up to ±10% Hz;

the fourth mode has a frequency of 243 up to ±10% Hz;

the fifth mode has a frequency of 321 up to ±10% Hz; and

the sixth mode has a frequency of 379 up to ±10% Hz.

4. The element of claim 1 , wherein the frequencies are within up to ±5% ranges.

5. 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 a span that is in a range of 27.5-28.5 inches, 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 13.0-14.0 inches, 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 34 up to ±10% Hz;

a second mode has a frequency of 90 up to ±10% Hz;

a third mode has a frequency of 178 up to ±10% Hz;

a fourth mode has a frequency of 222 up to ±10% Hz;

a fifth mode has a frequency of 307 up to ±10% Hz; and

a sixth mode has a frequency of 389 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.

6. The method according to claim 5 , wherein the first mode is a 1EB mode, the second mode is a 1EB/1T mode, the third mode is a 1T mode, the fourth mode is a 2EB mode, and the fifth mode includes a 2EB mode, and wherein the airfoil comprises an aluminum-based alloy, the aluminum-based alloy has a density of about 0.103 lb/in 3 , the aluminum-based alloy has a modulus of elasticity of about 10.4 Mpsi at room temperature.

7. 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 a span that is in a range of 27.5-28.5 inches;

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 13.0-14.0 inches; and

at least two of:

a first mode has a frequency of 34 up to ±10% Hz;

a second mode has a frequency of 90 up to ±10% Hz;

a third mode has a frequency of 178 up to ±10% Hz;

a fourth mode has a frequency of 222 up to ±10% Hz;

a fifth mode has a frequency of 307 up to ±10% Hz; and

a sixth mode has a frequency of 389 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 airfoil is provided in the fan section, the airfoil is part of a blade;

wherein the airfoil is made of an aluminum-based alloy with a density of about 0.103 lb/in 3 and with a modulus of elasticity of about 10.4 Mpsi at room temperature;

wherein the first mode is a 1EB mode, the second mode is a 1EB/1T mode, the third mode is a 1T mode, the fourth mode is a 2EB mode, and the fifth mode includes a 2EB mode, the 1EB and 2EB modes correspond to deflections substantially parallel to the thickness direction, and the 1T mode corresponds to twisting about the radial direction.