Oversizing Novel Aircraft Propulsion Systems for Power Redundancy

This paper expands the one-engine-inoperative conventional oversizing consideration to account for aircraft propulsion systems with multiple energy sources and thrust-generating media. Components in a generic hybrid propulsion system are categorized into power-generation, power-transmission and thrust-generation. For a given architecture, each possible single component failure is simulated to identify elements affected or eliminated by the respective loss of power, through the use of connection matrices. Failures are linked to losses in supplied and propulsive power, creating a list of oversizing factors for all individual components. Each element is oversized according to its corresponding maximum oversizing rate, defining the ideally redundant propulsion system. Case studies for conventional, all-electric and hybrid-electric powertrains highlight the need for balancing the number of components between minimum excess power and increasing the probability of a failure. Additionally, it is shown that asymmetrical configurations should not have major imbalance of power to avoid significant oversizing. The proposed methodology is applied to a 19-passenger, commuter aircraft. Increasing oversizing rate close to ideal leads to lower optimum energy consumption and increases redundancy. However, payload capacity penalties are required, up to 4 passengers for ideal oversizing. Heavier variants without penalties are up to 4% more efficient in terms of energy-per-weight in their carrying capacity against counterparts of the same oversize rate with reduced payload capacity. The proposed method maintains the principles of the conventional oversizing process, and highlights the tradeoffs needed between redundancy and performance in sizing novel propulsion systems.