Turbofan engine including a double gearbox assembly having a double gearbox engine parameter

An engine system for an aircraft, the engine system comprising:

• a first turbofan engine comprising:
• a first turbo-engine including a compressor section, a turbine section, and a combustor in fluid communication with the compressor section and the turbine section, the turbine section including a low-pressure turbine having a first low-pressure shaft and a plurality of low-pressure turbine stages;
• a first fan having a first fan shaft;
• and
• a double gearbox assembly, the first fan shaft being drivingly coupled to the first low-pressure shaft through the double gearbox assembly, wherein the first low-pressure shaft rotates in a counterclockwise direction and the first fan shaft rotates in the counterclockwise direction such that the first fan rotates in the counterclockwise direction, the double gearbox assembly comprising:
• a first stage gear assembly coupled to the first low-pressure shaft, the first stage gear assembly including a first stage sun gear, a plurality of first stage planet gears meshing with the first stage sun gear, and a first stage ring gear having a plurality of ring gear teeth and meshing with the plurality of first stage planet gears, and an interstage shaft;
• and
• a second stage gear assembly coupled to the interstage shaft, the second stage gear assembly including a second stage sun gear, a plurality of second stage planet gears meshing with the second stage sun gear, and a second stage ring gear having a plurality of ring gear teeth and meshing with the plurality of second stage planet gears, and an output shaft coupled to the first fan shaft,
• wherein the double gearbox assembly is characterized by a Double Gearbox Engine Parameter (DGEP) in a range from 150 kilograms to 650 kilograms, the DGEP being given by:
• k
• ×
• S
• ×
• ∑
• i
• =
• 1
• 2
• ⁢
• (
• P
• fan
• ×
• 10
• 6
• ×
• z
• i
• 376
• ×
• ω
• ring
• ⁢
• i
• ×
• n
• planetsi
• ×
• R
• ring
• ⁢
• i
• 2
• ×
• π
• ×
• R
• ring
• ⁢
• i
• 2
• z
• i
• 2
• ×
• (
• 18.5
• ×
• z
• i
• +
• 85.5625
• )
• )
• wherein k is a constant value based on a number of the plurality of first stage planet gears or the plurality of second stage planet gears, S is a number of the plurality of low-pressure turbine stages of the low-pressure turbine, i is the first stage gear assembly or the second stage gear assembly, Pfan is a power of the first fan at high-power conditions, ωring i is a rotational speed at high-power conditions of the first stage ring gear when i is 1 or the second stage ring gear when i is 2, nplanetsi is a number of the plurality of first stage planet gears when i is 1 or the plurality of second stage planet gears when i is 2, Rring i is a ring gear pitch radius of the first stage ring gear when i is 1 or the second stage ring gear when i is 2, and zi is a number of the plurality of ring gear teeth of the first stage ring gear when i is 1 or the second stage ring gear when i is 2;
• and
• a second turbofan engine comprising:
• a second turbo-engine including a compressor section, a turbine section, and a combustor in fluid communication with the compressor section and the turbine section, the turbine section including a second low-pressure shaft;
• a second fan having a second fan shaft;
• and
• a gearbox assembly comprising a gear assembly, the second fan shaft being drivingly coupled to the second low-pressure shaft through the gearbox assembly, wherein the second low-pressure shaft rotates in the counterclockwise direction and the second fan shaft rotates in a clockwise direction such that the second fan rotates in the clockwise direction.