To understand what the current level of electric airplane propulsion is with respect to large passenger airliners I developed the following question:
How many battery swaps would be required to fly the same route as the first non-stop transatlantic flight with an electric equivalent of a passenger aircraft able to transport +-600 passengers at once with a cruise speed of Mach 0.85?
To minimize the ambiguities regarding the question I made the following assumptions:
- The first non-stop transatlantic flight took place from Lester's Field, near St. Johns, Newfoundland on June 14,1919, and landed June 15,1919, at Clifden in Ireland. The time for the crossing was sixteen hours, twenty-seven minutes.
- It is assumed there is currently no battery technology that is able to perform the flight for 600 passengers without reloading during the flight, a mid-flight battery swap system is assumed.
- The battery swaps are assumed to be possible at 34.000 feat altitude at mach 0.85.
- The battery is assumed to be fully charged upon placement in the aircraft.
- A suitable runway can be built/is available at/near the departure and arrival destinations.
- Max thrusts required for take off and landing are ignored based on assistant launcher aircraft/rialguns. I.e. the aircraft is only considered in (optimal) cruise conditions.
- The batteries can be located, in fully charged state on any position on the surface of the globe along the route.
- Current (2020-06-30) battery technology is assumed. In particular the specs for the Pipistrel Velis Electro with 11.0 kWh, capable of delivering a constant 49 kW is assumed.
- A lithium battery density of 500 W/kg and 900 W/l is assumed. (Optimistic assumption of portability of technology that is not been proven in aviation applications despite cyclic acceleration loading, vibrational loading, temperature loading).
- The equivalent electric engines are assumed to be required to produce the same thrust in newtons as their combustion equivalent engines at 4x348=1392 kN.
- Speed of sound at cruising altitude of 34.000 ft of 240 m/s is assumed.
- A constant power usage of 1392.000x0.85x240=283968000W=283968 kW =~ 284 MW is assumed required to be continuously delivered by the electric jets.
- The mass penalty of the battery swap system is assumed 5000 kg. (Random unfounded optimistic estimate)
- The mass penalty is electric jet-engines is assumed to be twice the mass of the A380 Trent 970-84/970B-84 engine of 6246 kg is used, resulting in a mass penalty of 4x6246= 24.984 =~ 25000 kg.
- An additional mass penalty of 10.000 kg is assumed due to requirement of aircraft reconfiguration requirements. E.g. concerning electric cabling, lack of aircraft design optimization experience with large replaceable batteries in stead of wing-integrated fuel tanks. (Random optimisitic estimate/guess)
- The flight should be reproducible at least 95 % of the days of the past decade, to prevent estimating on unlikely favorable weather conditions.
Different assumptions can be made, please use comments to argue why assumptions could/should be adjusted, and keep answers for explaining how one can come up with the estimated amount of required battery swaps.