alt Hacker NewsI am really excited to se electric aviation start to enter the market. A lot of people point out the battery density / jet-A difference and it is valid, but it isn't the whole story. Jet-A has a much lower conversion to useful work than a battery, an electric power train (minus the batteries) has a lot of opportunity to shed weight (no bleed-air, fuel plumbing, less need to safety systems). There are a lot more opportunities to explore interesting airframes because electric can be placed in unique and more efficient ways (hence the eVTOL in this story). The basic physics change a lot too. We will see how high altitude flight shakes out but there is a big potential to go higher so that more efficiency can be gained, again needing less energy. The big point here is you can't simply compare electric to gas turbine and only swap the fuel for batteries. It is a totally different set of design parameters and it has so many amazing opportunities to be better.
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There's a hydrogen fuel cell version too that has been demonstrated.
This is one potential pathway towards cleaner aviation.
I'm much less optimistic. Even when factoring in the poor thermal efficiency of gas turbines (~30-40%) compared to electric (>90%), the usable specific energy gap remains immense. Jet-A still delivers roughly 14 times more useful work per kilogram than modern batteries. Removing fuel plumbing and tweaking airframes won't overcome that fundamental physics. Also the issue with the high-altitude efficiency argument is that batteries, unlike liquid fuel, don't lose mass during flight meaning the aircraft to haul its maximum takeoff weight from departure to arrival. It's a double whammy.
Comparing battery energy density to fuel energy density usually ignores the fact that combustion engines aren't that efficient. A great counterpoint is that if you apply the logic to a 60kwh EV, it should have the range of a 2 gallon petrol car. Which of course is not the case. Most medium sized petrol cars would have at least 8-10x that for a similar range to that 60kwh EV.
A more useful metric is $ per mile of range. Because if the vehicle can do the miles, that's all that matters. With the first generation of passenger drones their range isn't amazing. But their cost per mile is. And these Joby things have a useful enough range to do JFK to down town Manhattan.
I've been following the market a bit. There are a few interesting vehicles moving through certifications. Beta Aviation was touring all the airshows last summer with their ALIA CX300. It's a simplified ctol model of their vtol where they kept the pusher prop but removed the other props to speed up certification. So it's more like a conventional plane. It has a range of around 300 nautical miles depending on the battery configuration (modular). They flew it coast to coast in the US and all around Europe. It should get through certification by 2027 or so. Their vtol version has been flying for a while as well but will take longer to certify. It has less range because landing and taking off vertically just eats a chunk of battery. But once it is up in the air it flies pretty much the same as the ctol.
Of course the arrival of solid state batteries is going to shake things up. Everything that is close to being certified is flying without those. A potential doubling of energy densities is going to be a big deal. But certifying the batteries is going to take years.