>>1869158The range these airships have compared to the amount of fuel they carry already indicates they were working rather efficiently.
>>1862751If you do the math, you'll also see that at top speed (thus peak inneficiency) the graf zeppelin ii needa 3,56 Mw of power to attain 135 km/h, which amounts to around 78 kn of thrust or 7600 kgf if you assume a propeller efficiency of 80%.
Compare that to 232 000 kg of gross lift, and it adds up to a 30:1 lift to drag ratio. Given the way parasitic drag works, going twice as fast would reduce it to a 7:1, but at half speed it improves to 120:1, so airships are fuel efficient within their operating speeds even by modern standards.
