Airbreathing propulsion system trends.

Among trends in airbreathing propulsion, the priority is shown to belong to the goal of quieting engines to a level no greater than the natural background noise level of the environment in which they operate. For military engines, not so severely noise-constrained, the possibility of stoichiometric gas-turbine engines is shown to be within reach. Very high bypass ratio propfans are especially suitable for V/STOL aircraft. Evolution of reliable variable-geometry inlets and exhaust nozzles characterizes trends in the supersonic regime.