Helium is also heavier. For my dieselpunk setting, I came up with a design that uses helium as a safety "wrap" for hydrogen balloons to make air battleships. In the final scene where you take down the British Dreadnought, the British Admiral gets a squeaky voice as he cries out in rage.

A helium Hindenburg could lift like 3 tons while a hydrogen Hindenburg could do 10.

3 tons is barely enough for the engines and crew.