Abstract: A compact apparatus for simulating the in-flight aerodynamic performance of a multimission aircraft propulsion system of the gas turbine engine variety having an external envelope of a reduced size in relation to the engine to be simulated. The apparatus includes a turbine driven by externally generated, high pressure motive air which is drivingly connected to a compressor in the usual manner of a gas turbine engine. The flow of air pressurized by the compressor is mixed with a portion of the relatively higher pressure turbine motive air so as to generate a mixed flow having a generally uniform pressure profile entering the exhaust nozzle. The compressor, turbine, mixer and nozzle are sized to produce a pressure ratio across the apparatus and a nozzle flow function which are substantially identical to the engine to be simulated, though these components are of a reduced size in relation thereto.