Some speculation about the Eviation Alice, and electric airplanes in general
Here are the proposed specs for the Eviation Alice. It doesn’t say what the dry weight is, but the MTOW is 6,350 kg, compared to 3,629 kg for a Cessna Caravan. They claim 900 kWh of batteries, so if they were using Tesla packs that would be 5,730 kg. This would only leave 620 kg for the airframe and motors, not to mention crew and passengers, so Eviation must be using denser battery packs.
An empty Cessna Caravan weighs 2,145 kg so let’s just say this Alice weighs the same, and 12 passengers weigh 930 kg, and 130 kg for luggage. Then 6530 – (2145 + 930 + 130) = 3,325 kg for the battery, which means the battery specific energy has to go from 156 kWh/kg to 269 kWh/kg. That’s quite a leap! If we could shave 1,000 kg off the airframe using composites and ditching everything to do with the engine, then we’d only need 206 kWh/kg, which seems doable.
The Siemens SP260D aircraft motor produces 5.2 kW/kg (3.2 hp/lb), 261 kW from 50 kg. That’s probably the motor they’re using.
The Pipistrel Alpha Electro motor based on an Emrax motor produces 9 kW/kg and weighs 6 kg. Its batteries are kind of old in battery-tech years, so it just has 90 minutes of flying time. Magnax is claiming 12.5 kW/kg.
Then MagniX (no relation to Magnax) is only getting 4.7 kW/kg, more like the Siemens. I don’t know why Emrax is so much better. MagniX has been working with Cessna.
The Sunflyer 2 weighs 880 kg, has a Siemens SP70D 70kW motor, and has a range of 3.5 hours, with a cruise speed of 135 kts. For some reason they’ve taken down their website. I’ve read somewhere that Sunflyer’s battery cells are the 260 Wh/kg kind, but I don’t know the specific energy of their assembled battery packs.
The Sunflyer 4 will do 4.5 hours with a 105 kW motor and 150 kts cruise.
A lot of these commercial electric aircraft makers are going with hybrids. The Equator P2 Excursion is a light aircraft, but it shows one way. This Diamond DA40 with electric motors and a generator is another way, but the basic idea is – smallish batteries with a diesel or gas generator. The batteries give a takeoff boost so the engine can be smaller than an equivalent engine powered plane.
The best thing about electric motors for propulsion is that they make the airframe energy agnostic. Once you have the motors, you can use almost anything to power them – batteries, diesel generator, turbine generator, nuclear powered Stirling engine.