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Propulsion of airships

In recent years the advances in materials technology, coupled with the rising operating costs of conventional aircraft, have led to renewed interest in the airship as a means of fulfilling certain transportation requirements. This brief paper does not attempt to retell the story of the airship or to try and justify its present day use, this being far better left to the experts in this field, but considers the requirements and considerations to be taken into account when selecting a propulsion device. The propulsion devices considered are limited to open propellers and very low pressure ratio ducted fans.