R AMJET-POWERED engines have a history of over 100 years [1]. The secret to efficiency, safety, and performance of ramjet combustion systems has been the correct location and control of the terminal shock in the intake duct [2]. The position of the intake shock is affected by perturbations propagating upstream from the combustor [3] and from disturbances in the freestream [4]. These can lead to the familiar instability problems of unstart or buzz [5,6]. At the same time, these very instabilities can be controlled by pressure perturbations injected by suitably manipulating the exhaust nozzle throat area [7]. To properly evaluate such a control, it is necessary to obtain amodel for the ramjet engine including the intake, combustor, and exhaust nozzle. The issue of shock position control has always been an interesting one [8], but accurately sensing the position of the intake shock for the purpose of active control has been a challenge. In recent years, though, the problemhas attractedmuch attention [9,10], and building on the earlier work on the dynamics of shocks in ducts [3,11], models that may be used for designing intake shock position controllers have been obtained [12,13].However, itmay be noted that all thesemodels were limited to the intake alone and hence could not be directly used to study the effect of the exhaust nozzle throat area variation on the intake shock location. A model that couples the intake with the combustor and exhaust nozzle for a ramjet was first realized recently by our coworkers [14], and it was used [15] to derive a control law for the intake shock location using the nozzle throat area as input. A significant feature of the model in [14] was the use of time lags to capture the physics of upstream anddownstreampropagatingwaves between the intake and combustor. However, these time lags were applied to the primitive variables for simplicity instead of the specific pressure or entropy waves [12]. Second, despite the relatively low order of the global model in [14], the model for each component was multiparameter and nonlinear, in order to capture the various physical phenomena in the intake and combustor. Thus, in deriving the control law in [15], local linearized reduced-order models at several operating points had to be obtained using a system identification tool. The system identification is, unfortunately, a mathematical procedure that results in a set of states that cannot be easily related to the physical variables, thus masking the physical relationships inherent in the system. Control of the terminal shock positionwas obtained indirectly in [15] by defining a related parameter called intake backpressure margin. The present Note differs from these previous works in three significantways. First, wewrite an explicit equation for the dynamics of the intake shock location in a coupled model of the intake and the combustor plus nozzle. Second, a single time-lag parameter is obtained numerically, and applied directly to the shock position variable. Third, the various component models are written using standard quasi-one-dimensional flow relations in such a manner that the physical relationships they represent are apparent. These features make the present model more suitable for controller design with the objective of regulating the intake shock position; hence, it is called a control-oriented model.