This study seeks to gain understanding of the physics of supersonic inlet unstart using high speed schlieren, PIV and fast response pressure measurements. ; A simplified inlet/isolator model with plexiglass sidewalls is used. ; With further understanding of unstart, passive and active control methods involving vortex generators and vortex generator jets can be investigated.The dual-mode engine concept allows an engine to act as a ramjet at lower supersonic flight Mach numbers and then transition to a scramjet at higher supersonic to hypersonic flight Mach numbers. In dual-mode engines, the inlet and isolator provide the compression necessary for combustion. If the combustion pressure becomes larger than the maximum that can be provided by the inlet / isolator combination, the process of inlet unstart will occur. This transient process can result in large pressure loads, high drag and loss of combustion. The physics of unstart are not well understood. At our laboratory, unstart has been investigated using time resolved Schlieren combined with fast response pressure measurements.