Originally Posted by
petit plateau
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 ?
The best energy burn/passenger-km for conventional aircraft I could find was 259 wh/passenger-km (2.78L/100 passenger-km) and that number does account for inefficiencies of the engine, so I'm not sure how they arrive at the 167wh number; that's a massive improvement in flight energy consumption. An aircraft is an aircraft and a fuel burning machine will obviously reduce its weight as distance is traveled.