You have a good eye Dave, yet this is not anything created by the great engineer-statesman Enrico Forlanini. However, the F.5 had almost the exact same dimensions as the challenge airship – so you're in the ballpark. BTW, except for engines (2 vs. 4), the F.5 specs (and general appearance) were almost identical to the F.6 – the F.5 being the slightly larger of the two. The way to tell them apart is by the gondola. The F.6 having the noticeably longer, more streamlined car.