An AC electrical system for a vehicle and methods of operating the same are provided. In one aspect, an AC electrical system includes a first electric machine mechanically coupled with a first spool of a gas turbine engine and a second electric machine mechanically coupled with a second spool of the gas turbine engine. The system also includes a first AC bus and a second AC bus. A first electrical channel electrically couples the first electric machine to the first AC bus and a second electrical channel electrically couples the second electric machine to the second AC bus. The system also includes one or more connection links and one or more power converters for selectively electrically coupling the first and second electrical channels so that electrical power generated by one electric machine can be converted and shared with the other electric machine and electrical loads of the other channel.

A gas turbine engine and methods of operation include a low pressure electric motor-generator having an electrical assembly for electrical connection.

A gas turbine engine and methods of operation include a low pressure electric motor-generator having an electrical assembly for electrical connection.

According to an aspect, a method of providing internal shaft lubrication includes drip feeding a lubricant to a feed tube within a central bore of a shaft body. The lubricant is urged along a lubrication flow path including at least one rifling groove on an inner wall of the shaft body formed by the central bore and a plurality of lubrication holes axially distributed along the shaft body that fluidically connects the inner wall with an outer wall of the shaft body. The lubricant is sprayed out of the lubrication holes responsive to rotation of the shaft body.

According to an aspect, a method of providing internal shaft lubrication includes drip feeding a lubricant to a feed tube within a central bore of a shaft body. The lubricant is urged along a lubrication flow path including at least one rifling groove on an inner wall of the shaft body formed by the central bore and a plurality of lubrication holes axially distributed along the shaft body that fluidically connects the inner wall with an outer wall of the shaft body. The lubricant is sprayed out of the lubrication holes responsive to rotation of the shaft body.

An exemplary gas turbine engine assembly includes a first spool having a first turbine operatively mounted to a first turbine shaft, and a second spool having a second turbine operatively mounted to a second turbine shaft. The first and second turbines are mounted for rotation about a common rotational axis within an engine static structure. The first and second turbine shafts are coaxial with one another. First and second towershafts are respectively coupled to the first and second turbine shafts. An accessory drive gearbox has a set of gears. A compressor is driven by the first towershaft. The engine assembly further includes a starter generator assembly, and a transmission coupling the starter generator assembly to the first set of gears. The transmission is transitionable between a first mode where the starter generator assembly is driven at a first speed relative to the second towershaft, and a second mode where the starter generator assembly is driven at a different, second speed relative to the second towershaft.

An exemplary gas turbine engine assembly includes a first spool having a first turbine operatively mounted to a first turbine shaft, and a second spool having a second turbine operatively mounted to a second turbine shaft. The first and second turbines are mounted for rotation about a common rotational axis within an engine static structure. The first and second turbine shafts are coaxial with one another. First and second towershafts are respectively coupled to the first and second turbine shafts. An accessory drive gearbox has a set of gears. A compressor is driven by the first towershaft. The engine assembly further includes a starter generator assembly, and a transmission coupling the starter generator assembly to the first set of gears. The transmission is transitionable between a first mode where the starter generator assembly is driven at a first speed relative to the second towershaft, and a second mode where the starter generator assembly is driven at a different, second speed relative to the second towershaft.

An embodiment of an engine assembly includes a plurality of offtakes powered by a combustion turbine engine having a high spool and at least one lower spool, and a controller configured to operate the combustion turbine engine through a range between a first low-idle mode, a second high idle mode, and a maximum takeoff power rating mode. The controller operates the engine in the low-idle mode by directing at least a first portion of power from the at least one lower spool to the plurality of offtakes, and wherein the controller operates the engine in the high idle mode by increasing a speed of the high spool relative to a speed of the high spool in the low-idle mode, thereby increasing a compressor outlet (T.sub.3) temperature in the high idle mode relative to a T.sub.3 temperature in the low-idle mode.

An embodiment of an engine assembly includes a plurality of offtakes powered by a combustion turbine engine having a high spool and at least one lower spool, and a controller configured to operate the combustion turbine engine through a range between a first low-idle mode, a second high idle mode, and a maximum takeoff power rating mode. The controller operates the engine in the low-idle mode by directing at least a first portion of power from the at least one lower spool to the plurality of offtakes, and wherein the controller operates the engine in the high idle mode by increasing a speed of the high spool relative to a speed of the high spool in the low-idle mode, thereby increasing a compressor outlet (T.sub.3) temperature in the high idle mode relative to a T.sub.3 temperature in the low-idle mode.

An apparatus and method for a generator for generating power having a rotary union between a rotor and a stator, the rotary union comprising a first fluid passage having a converging nozzle and located within the stator having a first inlet and a first outlet, a second fluid passage having a diverging nozzle and located within the rotor and having a second inlet and a second outlet, the second inlet is aligned with the first outlet and at least one gap located between the rotor and stator.