To enhance the endurance and energy utilization efficiency of electric propulsion aircraft (EPA), this article constructs an integrated energy system (IES) architecture for EPA and, on this basis, proposes an energy management strategy (EMS) that considers both transient and steady-state operating conditions. The IES includes super-capacitors (SC), batteries, fuel cells (FCs), open winding permanent magnet synchronous generator, and the corresponding power converters. Under transient conditions with varying loads, low-frequency power is automatically directed to the FC and generator, medium-frequency power is allocated to the battery, and high-frequency power is assigned to the SC. This dynamic power distribution is facilitated by a decentralized droop control within the EMS framework. In addition, the proposed strategy promotes the recovery of the state of charge (SoC) of SCs and batteries, stabilizes the bus voltage, and effectively absorbs regenerative energy. In a steady-state scenario, the EMS proposed in this article optimizes the output power of FC, battery, and generator in a distributed manner, ensuring the system's efficiency and cost-effectiveness. Finally, an experimental platform is established for the proposed IES architecture, and the feasibility of the proposed EMS is validated.