This paper presents the details of an engine emulation system utilized within a Hardware-in-the-Loop (HIL) test environment for aircraft power systems. The paper focuses on the software and hardware interfaces that enable the coupling of the engine model and the generator hardware. In particular, the rotor dynamics model that provides the critical link between the modeled dynamics of the engine and the measured dynamics of the generator is described in detail. Careful consideration for the measured torque is included since the measurement contains inertial effects as well as torsional resonances. In addition, the rotor model is equipped with the ability to apply power and speed scaling between the engine and generator. This scaling approach provides significant flexibility that can be useful when hardware resources are limited such that a direct engine-generator match is not possible or when one wants to evaluate turboshaft engine dynamics for a variety of applications and power levels. Depending on what type of scaling is used, there may be an effect on the maximum power the drive stand must provide to fully emulate engine transients. Explicit torque/power requirements are given, along with an evaluation of the existing drive stand's emulation capabilities.