Method for setting a gear ratio of a fan drive gear system of a gas turbine engine

A gas turbine engine comprising:

• an engine centerline longitudinal axis;
• a fan section including a fan with a plurality of fan blades and rotatable about the engine centerline longitudinal axis, wherein the fan has a low corrected fan tip speed less than 1400 ft/sec, wherein the low corrected fan tip speed is an actual fan tip speed at an ambient temperature divided by [(Tram ° R)/(518.7° R)]0.5, where Tram represents the ambient temperature in degrees Rankine;
• a bypass ratio greater than 11.0 and less than 22.0;
• a fan pressure ratio less than 1.52, wherein the fan pressure ratio is measured across a fan blade alone;
• a speed reduction device comprising a gear system, wherein the gear system is a star gear system with a ring gear, a sun gear, and a star gear ratio, and the star gear ratio is determined by measuring a diameter of the ring gear and dividing that diameter by the diameter of the sun gear;
• a low pressure turbine in communication with a first shaft;
• and
• a high pressure turbine in communication with a second shaft;
• wherein the first shaft and second shaft are concentric and mounted via at least one of a plurality of bearing systems for rotation about the engine centerline longitudinal axis, and the first shaft is in communication with the fan through the speed reduction device;
• wherein the low pressure turbine includes four stages;
• wherein the low pressure turbine includes at least one rotor constrained by a first stress level, at least one of the plurality of fan blades of the fan constrained by a second stress level and having a fan tip speed boundary condition, and the star gear ratio is configured such that in operation the at least one of the plurality of fan blades does not exceed the fan tip speed boundary condition or the second stress level, and the at least one low pressure turbine rotor does not exceed the first stress level;
• and
• wherein the high pressure turbine includes two stages.

A gas turbine engine comprising:

• an engine centerline longitudinal axis;
• a fan section including a fan with a plurality of fan blades and rotatable about the engine centerline longitudinal axis;
• a low corrected fan tip speed less than 1150 ft/sec, wherein the low corrected fan tip speed is an actual fan tip speed at an ambient temperature divided by [(Tram ° R)/(518.7° R)]0.5, where Tram represents the ambient temperature in degrees Rankine;
• a bypass ratio of greater than 11.0 and less than 22.0;
• a speed reduction device comprising a gear system with a gear reduction ratio;
• a first turbine in communication with a first shaft;
• and
• a second turbine in communication with a second shaft;
• wherein the first shaft and second shaft are concentric and mounted via at least one of a plurality of bearing systems for rotation about the engine centerline longitudinal axis, and the first shaft is in communication with the fan through the speed reduction device;
• wherein the first turbine includes at least three stages and no more than four stages;
• and
• wherein the first turbine includes at least one rotor constrained by a first stress level, at least one of the plurality of fan blades of the fan constrained by a second stress level and having a fan tip speed boundary condition, and the gear reduction ratio is configured such that in operation the at least one of the plurality of fan blades does not exceed the fan tip speed boundary condition or the second stress level, and the at least one first turbine rotor does not exceed the first stress level.

A gas turbine engine comprising:

• an engine centerline longitudinal axis;
• a fan section including a fan with a plurality of fan blades and rotatable about the engine centerline longitudinal axis;
• a low corrected fan tip speed less than 1400 ft/sec, wherein the low corrected fan tip speed is an actual fan tip speed at an ambient temperature divided by [(Tram ° R)/(518.7° R)]0.5, where Tram represents the ambient temperature in degrees Rankine;
• a bypass ratio greater than 11 and less than 22;
• a speed reduction device comprising a gear system with a gear reduction ratio;
• a low pressure turbine in communication with a first shaft;
• and
• a high pressure turbine in communication with a second shaft;
• wherein the first shaft and second shaft are concentric and mounted via at least one of a plurality of bearing systems for rotation about the engine centerline longitudinal axis, and the first shaft is in communication with the fan through the speed reduction device;
• and
• wherein the low pressure turbine includes four stages;
• and
• wherein the low pressure turbine includes at least one rotor constrained by a first stress level, at least one of the plurality of fan blades of the fan constrained by a second stress level and having a fan tip speed boundary condition, and the gear reduction ratio is configured such that in operation the at least one of the plurality of fan blades does not exceed the fan tip speed boundary condition or the second stress level, and the at least one low pressure turbine rotor does not exceed the first stress level.