A study on a rotating detonation engines (RDE) having the advantage of high frequency operation (1~100 kHz) and simple structure has been carried out in many research groups for the practical use toward a rocket engine. However, there are many unsolved parts about internal flow of a RDE, and the state of its channel exit has not been solved exactly. In this study, we used gas ethylene and gas oxygen as propellant. A slide mechanism for thrust measurement was developed. We will evaluate and the thrust performance and the state of channel exit of a RDE by the nozzle shape. We performed combustion test of a RDE with a conical-shape tail. As a results, thrust of a RDE with a conical-shape tail was achieved 101 ~ 308 N.