US Patent 12071894 Aircraft heat management

A method of operating a gas turbine engine including an engine core and turbine, a compressor, a combustor arranged to combust a fuel, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core; a fan shaft; a main gearbox that receives an input from the core shaft and outputs drive to the fan via the fan shaft, the main gearbox including gears and journal bearings; a recirculating lubrication system arranged to supply oil to lubricate the gears and journal bearings, the lubrication system including a first oil tank arranged to supply oil to the gears and journal bearings and a second oil tank arranged to supply oil to the journal bearings only. The method includes, at cruise conditions: transferring 200-600 kJ/m