Propulsion requirements for the next generation of civil aircraft are examined and some new and quite demanding needs are defined—larger engine sizes, higher takeoff thrusts, and much lower noise levels. The remarkable propulsion advances over the past two decades are charted and, from these, projections are made for the next round of improvements. All of the propulsion systems considered incorporate advanced technology gas turbine engines coupled with propulsors having a broad range of bypass ratio—from fans to propellers. This encompasses a new class of high-thrust, low-noise propulsor—the Prop-Fan—which is introduced as a needed intermediate propulsor between today's fans and propellers. This widening scope of available propulsors is shown to offer the aircraft designer much more flexibility in powerplant selection and a better opportunity to optimalize his design. Although the primary focus is on civil aviation, wherever appropriate the commonality with military requirements has been indicated.

R. E. Neitzel

Papers

Noise Considerations in the Design of Advanced Subsonic Transport Turbofan Engines