Originally Posted by
Winemaker
A quick calculation using the numbers in the article as to range, passengers, and battery energy density, suggests a battery to fly 800 km would mass about 33,500 kg. This does not include any reserve; with a 200 km reserve the mass is about 42,000 kg. One aspect of battery power is the landing aircraft weighs the same as the takeoff craft (with a tiny loss due to quantum effects that I will ignore). The kwh/passenger/km and energy density numbers also seem to be optimistic.
Thanks.
To be fair with a 76 tonne aircraft they themselves come up with a 35 tonne battery, so your 42-tonne calc (including reserve) seems to be in wild agreement.
As to the reserve fraction that is where they go with a gasturbine genset and liquid fuel so as to minimise emergency ordinarily unused weight. That is exactly the strategy I use when designing similar energy systems so I am not surprised by it. So that leaves 7 tonnes (your figure 42 - 35 = 7) of not-required reserve battery & liquid fuel. If you look at Fig 3 that looks to be about a 5% mass fraction, or 3.8 tonnes for emgy turbine + fuel, so a useful saving on your 7 tonne estimate. It seems your numbers are directionally in agreement with their numbers.
Are there any numbers that are identifiably plain wrong ?