Aerodynamics of a Single-Engine Aircraft Retrofit for Hydrogen-Electric Propulsion

Hydrogen-electric propulsion systems (HEPS) are being developed to achieve net-zero flight in the near future. Key to accelerating the entry-into-service is the retrofit of HEPS onto existing airframes to reduce the certification timeline associated with clean sheet aircraft. Maintaining existing payload volume for operators of aircraft such as the Cessna C208B Grand Caravan will allow for a commercially viable solution. The volumetric energy density of compressed gaseous hydrogen or cryogenic liquid hydrogen and the increased cooling requirements of proton-exchange membrane fuel cells both lead to modifications mounted externally to the fuselage of the retrofitted aircraft. A 1:10 scale wind tunnel model was developed under a collaboration between the University of Bath and ZeroAvia. The additively manufactured model was assessed in a low-speed closed-return wind tunnel, with comparison to aerodynamic coefficients derived from publicly-available C208 data. The test article includes provisions for scaled propellers of 10" diameter with a range of pitch values. Simulated HEPS modifications of approximate size were tested on the belly of the aircraft, where an existing airframe cargo pod is mounted. The increased drag and modified trim of the C208 have implications on the design of the aerodynamic fairings that must contain the HEPS modifications.