Hypersonic propulsion research has been a focus of the NASA aeronautics program for years. Previous high-speed cruise and space access programs have examined the problems of inlet design for hybrid systems, mainly by addressing one part of the flight envelope only. The proposed program will leverage existing technology by utilizing design data for the high-speed inlet for a Mach 5 over-under turbojet/ramjet propulsion system. The proposed effort will identify a variable geometry system that will effect mode transition between modes. An experimental research effort will be designed, and requirements for the research hardware (aerodynamic design and functionality) will be developed sufficiently to commence mechanical design early in a follow-on Phase II effort. The objective of the Phase II effort will be to experimentally demonstrate operation of the dual-flow inlet system during mode transition. Mode transition of hypersonic inlet systems with dual flow paths represents one of the greatest challenges facing hypersonic propulsion system designers. The proposed research will provide design approaches to these problems, for which few workable solutions have yet been identified. The innovations in hypersonic inlet design technology provided by this and follow-on research will provide enabling technology required to bring low-cost hypersonic flight closer to practical reality.