Since wind tunnel tests showed that a 16-side transverse section had about the same drag as a circular one, both R100 and R101 used a smaller number of longitudinal girders than previous airships to simplify stress calculations. Even so, the calculations for the transverse frames required hand computation that took two or three months to produce a solution for each frame. The thoroughness of the stressing calculations was a consequence of new Air Ministry criteria for the strengths required of airships, formulated after the catastrophic structural failure of R38 in 1921. Fewer longitudinal girders resulted in larger unsupported panels of fabric in the envelope, and flight trials were to prove that the R100's covering was barely adequate. The envelope of R101 was also unsatisfactory and a failure in its cover was possibly a cause of its crash.