Gas turbine engines and epicyclic gearboxes with planet gear clearances

A gas turbine engine comprising:

• a gearbox assembly mechanically coupled to an LP shaft of the gas turbine engine, wherein the gearbox assembly comprises a sun gear, a ring gear, a carrier, and a plurality of planet gears arranged in a planetary configuration, wherein each of the plurality of planet gears comprises:
• a bearing pin comprising a pin outer surface;
• an annular planet gear rim comprising an inner surface, wherein the inner surface and the pin outer surface define a clearance, wherein the clearance is greater than zero when a radial component force, a pinch component force, a tangential component force, and a centrifugal component force are applied to the planet gear;
• a planet gear bending stress neutral axis radius, wherein the planet gear bending stress neutral axis radius is a radius where stresses and strains within the annular planet gear rim are zero when the radial component force, the pinch component force, the tangential component force, and the centrifugal component force are applied to the planet gear;
• and
• a pin clearance parameter defined by:
• PCP
• =
• K
• 1
• c
• r
• ⁢
• GR
• GR
• -
• 2
• ⁢
• r
• p
• 2
• [
• K
• 2
• ⁢
• r
• p
• 3
• ⁢
• Ω
• fan
• 3
• -
• HP
• fan
• N
• p
• ⁢
• (
• GR
• -
• 2
• GR
• )
• 2
• ]
• wherein “PCP” is the pin clearance parameter in rpm, “cr” is the clearance in inches, “GR” is a gear ratio of the gearbox assembly, “rp” is the planet gear bending stress neutral axis radius in inches, “Np” is a number of the plurality of planet gears, “HPfan” is a fan power of the gas turbine engine in horsepower at takeoff conditions, “Ωfan” is a fan speed of the gas turbine engine in rpm at takeoff conditions, K1 is a first constant of 1.96×10−5 per horsepower-minute-inch, and K2 is a second constant of 4.91×10−9 horsepower-minutes cubed per cubic inch, and
• wherein the pin clearance parameter is greater than or equal to zero rpm and less than or equal to 3,334 rpm;
• and
• a lubricant system configured to supply a lubricant to the gearbox assembly, the lubricant system comprising:
• a supply line;
• a first sensing component configured to measure a lubricant temperature at a first sensing position upstream of the gearbox assembly;
• and
• a second sensing component configured to measure a lubricant temperature at a second sensing position downstream of the gearbox assembly;
• wherein the lubricant system is configured to determine a difference of the lubricant temperature measured at the first sensing position and the lubricant temperature measured at the second sensing position, and
• wherein the lubricant system is configured to increase a flow rate of the lubricant through a component supply line if the difference of the lubricant temperature measured at the first sensing position and the lubricant temperature measured at the second sensing position exceeds a predetermined threshold lubricant temperature difference.