For an Unmanned Aerial Vehicle (UAV) performing a mission, any failure of the flight control system can result in fatal disaster. Therefore, reliability requirement for UAV flight control system becomes increasingly important and then the redundancy technology is considered as a solution to enhance system reliability. This paper studies the designs of reliability, system architecture, and redundancy management logic for UAV flight control system. Therefore, a reliable federated architecture design for triple redundant UAV flight control system is introduced, in which the distributed hardware design combined with centralized software framework was adopted as well. The number of subsystems in the case study is more than that of centralized architecture and less for distributed architecture. Next, the fault detection and fault tolerant design can be achieved, and simultaneously the design problems associated with distributed software framework was reduced. Furthermore, by using the distributed hardware, system's reliability requirement of single hardware module was decreased. Consequently, the goal of high reliability for the entire system reached. Finally, FlexRay bus with time-trigger mechanism was chosen to simulate the communication of such a federated architecture designed. The experimental results show that the design is reasonable and satisfy the high reliability, high performance-price ratio and high expandability requirements of UAV flight control system.