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

Abstract

A gas turbine engine includes a fan section including a fan rotatable about an axis of rotation of the gas turbine engine. A speed reduction device is in communication with the fan. The speed reduction device includes a star drive gear system with a star gear ratio of at least 1.5. A fan blade tip speed of the fan is less than 1400 fps. A bypass ratio is between about 11.0 and about 22.0.

What is claimed is: 
     
         1 . A gas turbine engine comprising:
 a fan section including a fan rotatable about an axis of rotation of the gas turbine engine;   a speed reduction device in communication with the fan, wherein the speed reduction device includes a star drive gear system with a star gear ratio of at least 1.5,   wherein a fan blade tip speed of the fan is less than 1400 fps; and a bypass ratio is between about 11.0 and about 22.0.   
     
     
         2 . The gas turbine engine of  claim 1 , wherein the speed reduction device includes a star gear system gear ratio of at least 2.6. 
     
     
         3 . The gas turbine engine of  claim 2 , wherein the speed reduction device includes a system gear ratio less than or equal to 4.1. 
     
     
         4 . The gas turbine engine of  claim 1 , wherein the star system includes a sun gear, a plurality of star gears, a ring gear, and a carrier. 
     
     
         5 . The gas turbine engine of  claim 4 , wherein each of the plurality of star gears includes at least one bearing. 
     
     
         6 . The gas turbine engine of  claim 4 , wherein the carrier is fixed from rotation. 
     
     
         7 . The gas turbine engine of  claim 4 , wherein a low pressure turbine is mechanically attached to the sun gear. 
     
     
         8 . The gas turbine engine of  claim 4 , wherein a fan section is mechanically attached to the ring gear. 
     
     
         9 . The gas turbine engine of  claim 1 , wherein an input of the speed reduction device is rotatable in a first direction and an output of the speed reduction device is rotatable in a second direction opposite to the first direction. 
     
     
         10 . The gas turbine engine of  claim 1 , including a low pressure turbine section in communication with the speed reduction device, wherein the low pressure turbine section includes at least three stages and no more than four stages. 
     
     
         11 . The gas turbine engine of  claim 10 , wherein the fan blade tip speed of the fan is greater than 1000 fps. 
     
     
         12 . The gas turbine engine as recited in  claim 1 , further comprising a low pressure turbine which is one of three turbine rotors, and the low pressure turbine drives the fan section and the other two of the three turbine rotors each drive a compressor section. 
     
     
         13 . The gas turbine engine as recited in  claim 1 , further comprising a high pressure turbine, with each of a low pressure turbine and the high pressure turbine driving a compressor rotor. 
     
     
         14 . The gas turbine engine as recited in  claim 13 , wherein the speed reduction device is positioned intermediate a compressor rotor driven by the low pressure turbine and the fan section. 
     
     
         15 . The gas turbine engine as recited in  claim 13 , wherein the speed reduction device is positioned intermediate the low pressure turbine and the compressor rotor driven by the low pressure turbine.