Advanced technology engine

Advanced technology engine is a turbine engine that allows different turbines to spin at different, individually optimum speeds, instead of at one speed for all. It became common in the 21st century. It emerged on larger airplanes, before finding other applications.

Details
One version has three drive shafts instead of the usual one. This allows the three sets of blades to revolve at different speeds. An intermediate design is a twin-spool engine, allowing two different speeds. ATE advantages allow lower noise levels.

Rolls Royce Ultrafan
The Rolls Royce Ultrafan is the largest and most efficient engine to allow multiple turbine speeds. The turbines behind the main fan are small and allow more air to pass straight through, while a planetary gearbox "allows the main fan to spin slower and the compressors to spin faster, putting each in their optimal zones."

Other geared turbofans
Geared turbofans are also used in the following engines, some still in development: Garrett TFE731, Lycoming ALF 502/LF 507, Pratt & Whitney PW1000G, Turbomeca Astafan, and Turbomeca Aspin, and Aviadvigatel PD-18R.

Astro Mechanica
In 2024 this startup announced its TurboElectric Adaptive Engine. Instead of a fixed gearbox, it uses an electric motor to turn the turbine(s) behind the fan at an ideal speed for each phase of flight. The company claimed it would support efficient take-off, subsonic, supersonic, and hypersonic speeds. The electric motor is powered by a generator in turn powered by a turbine. The approach relies on the improved power density of novel electric motors such as yokeless dual-rotor axial flux motors that offer far more kw/kg than conventional designs that were too heavy for such an application.

Air flows in through a turbogenerator to produce electric power to power an electric motor. The electric motor adaptively controls the propulsion unit, allowing it to behave like a turbofan, turbojet, or ramjet depending on airspeed. In effect the engine can operate at any point along the specific impulse (Isp) curve - high Isp at low speed or low Isp at high speed.

It is in some respects similar to turbo-electric marine engines that allow propellers to turn at a different speed than the steam turbines that power them.