Pre-compression by the windward surface of the aerospace plane is necessary for scramjet operation. However, this pre-compression causes spillage from the high-pressure windward surface toward the sides of the plane. In order to examine the effects of this side-spillage, the performance of a scramjet engine was evaluated using a 1-D flow model, and payload to the low earth orbit estimated using an aerospace plane flight simulation. Prior to the simulation, tests with scramjet inlet models were conducted in a Mach 4 wind tunnel to identify the primary features of the side-spillage to assist in the simulation. The models were inclined from the flow direction to simulate the skewed flow near the side of the plane during side-spillage, and the experiments proved that the aerodynamic performance of the inlet was not affected by the inclination for the entrance Mach number given to the models. However, the mass capture ratio decreased due to reduction in the density of airflow as a result of the expansion. In the numerical estimate, sidespillage was modeled not to reduce the performance of the inlet, but to reduce mass flow to the inlet. The resulting decrease in airflow delivered to the engine due to spillage reduced thrust by 15%, while the corresponding payload decreased around 60%. Side fences were effective in preventing spillage.

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There are three typical configurations for integrating the scramjet into the airframe of aerospace planes. They are (1) the whole engine is on the windward ramp surface of the airframe, (2) the engine is located downstream of the forebody ramp where the surface of the airframe is parallel to the airframe axis, and (3) the inlet entrance is on the ramp surface with the following engine parts parallel to the airframe axis. To examine the effect of the integrating forms on the engine performance, several types of the inlet models were tested in a wind tunnel, and simulations of the scramjet engine and the flight of the aerospace plane were conducted. The experimental results showed that the first and the third configurations showed better mass capture. In the second configuration, the pre-compression effect was neutralized by the expansion fan from the corner of the downstream end of the ramp. All configurations showed similar levels of kinetic energy efficiencies. The simulation based on the experimental results showed that the third configuration produced the best engine thrust and the least airframe drag. On the other hand, in the second configuration, the payload became negative. Thus, it is recommended that the inlet should be located on the windward ramp surface of the vehicle to inhale the precompressed air, and the following engine components should be parallel to the airframe axis to reduce the cowl drag and to increase the thrust at the external nozzle.

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