Certification considerations for the configuration of a hydrogen-fuelled aeroplane

Abstract

AbstractReplacing kerosene with hydrogen as a fuel for propelling aeroplanes will undoubtably have ramifications for the existing certification basis and the necessary means of compliance. What this paper attempts to do is explain how a future hydrogen-powered aeroplane could be certified and how this will influence the aircraft’s design. Emphasis has been placed on the safety of hydrogen with regards flammability, ignition energy, cryogenic states and crashworthiness. The influence of certification on a future hydrogen-fuelled aeroplane’s configuration has been established. Lessons learnt from rockets are limited in scope. Consideration of hydrogen’s cryogenic and ambient temperature properties has established some fundamental safety principles. Fuel system crashworthiness influence on certification has been examined. An explosion prevention certification scheme has been developed. It is proposed to exclude oxygen from the fuel system and avoid accumulation of leaked or permeated hydrogen from adjacent zones. Three generic hydrogen-fuelled configurations have been considered for certification: adapting conventional airliner design, hydrogen-electric (fuel cell) propulsion and an unconventional approach. Hydrogen as a safe gas turbine fuel has been examined in technical and environmental terms. Further experimental work to close knowledge gaps in the aviation use of hydrogen has been suggested. In conclusion the necessary changes to the certification basis are outlined. Comments as to what the configuration of a future hydrogen-fuelled aeroplane might look like are provided. These observations are based on analysis of hydrogen’s properties, the existing certification basis, knowledge gaps, and what Special Conditions and Acceptable Means of Compliance might emerge in a future design Type Certification.