To reduce the cost of space transportation, JAXA continues studying fully reusable space transporters with hypersonic airbreathing engines. To fulfill the requirement of acceleration capability from zero to hypersonic speed, the rocket-based combined cycle (RBCC) engine is one of the promising candidates and has been studied in JAXA Kakuda Space Center. In the researches of the engine, the specialized wind tunnel for the airbreathing engines (Ramjet Engine Test Facility, RJTF) has been always a practical tool to investigate the performance and detailed flow phenomena inside the engine. However, to simulate the hypersonic, high enthalpy flow, the wind tunnel uses gas hydrogen and oxygen to heat the flow, resulting the air contamination by water which affects to the combustion phenomenon. To clarify the effect of the contamination, series of the cooperative researches have been conducted in JAXA and universities. The final goal of the researches are to create the adjustment tools for contamination effects, which ensure more accurate estimation for the performances of engine in the real flight. For validating the tools, the real flight data are quite essential. In the researches, a flight experiment had been also planned to get combustion data during hypersonic flight to compare the results in the wind tunnel and estimated values by the tools. In this report, the flight experiment with “S-520-RD1” is described. In early phase of the development, several rocket systems, flight trajectories and flight test bed configurations were explored. For the experiment, the attitude control of the flight test bed was required and it was achieved by the rhumb line device. The flight conditions inwhich actual combustion experiment was conducted were determined by the air data system specifically designed and integrated into the test bed. The duration time for the combustion test reached as long as 5.8 sec, with highest Mach No. of 5.8. The summery of the results of combustion test is also presented.