At the May 2017 EBACE, Aerion announced its selection of GE Aviation to power the Aerion AS2 supersonic business jet. GE then launched the Affinity program. The final engine configuration is a core with billions of operational hours – suggesting the CFM56 – and a new low-pressure section optimised for supersonic speed. The CFM56 is derived from the B-1's GE F101. In February 2018, Aerion released the GE engine configuration. Thrust will be reduced at takeoff to meet Chapter 5noise regulations, requiring a longer balanced field takeoff as an acceptable compromise. Chapter 5 applies from 2018 to over 120,000 lb aircraft and all aircraft from 2021. The initial design of its Affinity medium-bypass-ratio turbofan was completed by October 2018. Its detailed design review should be completed by 2020 for the first prototype production.
Design
GE Aviation needs to develop a configuration accommodating reasonably well requirements for supersonic speed, subsonic speed and noise levels. Managing the high intake temperatures at high altitudes is a key challenge for the initial design. An engine for supersonic flight needs a lower bypass ratio than modern turbofans, having a higher flow speed for better efficiency. This is limited by noise regulations at takeoff, and a lower compression core like the CFM56 is better suited to higher temperatures encountered supersonically. The engine is a compromise between a big core for power and a small fan for wave drag, and Mach 1.4 is a compromise between higher speed and enough range. The high-pressure core is derived from the nine-stage compressor and single-stage turbine of the CFM56, matched to a new low-pressure section optimised for supersonic speed with a 133 cm diameter fan instead of the 155-173 cm fan of the 6:1 bypass ratio CFM56. The twin-shaft, twin-fan engine with FADEC has a service ceiling of 18,300 m. It lacks an afterburner, and has a combustor with advanced coatings and uses additive manufacturing technologies. The GE Affinity has a nine-stage HP compressor, a single-stage HP turbine and a two-stage low-pressure turbine. Preceded by fixed inlet guide vanes with movable flaps, the twin blisked fans have wide-chord titanium blades. The exhaust mixer is similar to the GE Passportceramic matrix composite design. The Mach 1.4-to-1.6 speed requires no variable-geometry inlet and the variable-area nozzle has a cone moving longitudinally, replacing a convergent-divergent nozzle. The bypass ratio is around 3 to lower the ram drag, and it should produce at Mach 1.4 and FL500, with a cruise fuel consumption increased by 50% over the Mach 0.78 CFM56-5.
