Analysis of load tape constrained pneumatic envelopes

Abstract

This paper demonstrates with the aid of non-linear finite element analysis that the global load canying function in a pneumatic envelope, specifically in a super-pressure balloon, can be assigned to linear structural elements, The skins primary function is to transmit loads over the short span that separates the load tapes. In the proposed designs the strength requirements for the skin are significantly lower than in a spherical super-pressure balloon of the same capacity. The silhouette of the proposed design is that of a “natural shape” zero-hoop-stress balloon. It is demonstrated that the stiffness ratio of the load tape vs. the skin plays an important role. The higher this ratio the more complete the global load carrying function of the load tapes, and for large enough ratios any further increase in load tape stiffness is irrelevant. Three classes of design are investigated. One class relies on elastic effects alone to achieve the desired result while the others use some lack of fit. It is also shown that the payload can be introduced through the nadir fitting. This avoids the troublesome load introduction detail of current superpressure balloon designs,