Comment by jillesvangurp
8 hours ago
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.
> Because if the vehicle can do the miles, that's all that matters.
Unfortunately that's probably going to stay fossil for a while. What might matter is things like local ordinances prohibiting it on AQI grounds (especially things like leaded fuel in Cessnas!), as well as more dramatic questions like shortages.
(we're probably never going to get a carbon tax on jet fuel, too much coordination required)
> Because if the vehicle can do the miles, that's all that matters
You conveniently forgot about climate change.
It also very much matters that my grandchildren will be able to breath, will have food to eat, won’t have to live underwater and won’t depend on wars in faraway lands.
If we can synthesize jet fuel cheaply with renewable electricity it's carbon neutral.
You are ignoring the second variable on the consumption of energy dense materials. Weight.
It correlates to the energy density of course, but, weight directly goes into the power consumption calculations for vehicles. Efficiency is just a multiplier afterwards.
You can only ignore weight in non-mobile battery applications, i.e. grid applications.
It is a multi-variate problem and petrol currently wins out by a wide margin.
>Comparing battery energy density to fuel energy density usually ignores the fact that combustion engines aren't that efficient.
>>Jet-A has a much lower conversion to useful work than a battery
Jet-A that has been combusted doesn't require any lift.
Edit: Since I have an aerospace engineering degree, I'll post the 100 level concept. https://web.mit.edu/16.unified/www/FALL/thermodynamics/notes...
But at the same time you had to design an aircraft to be able to shed that much weight and handle a load that sloshes around. That has cost. Again though, the core point is you can't compare directly. It is more about the final design and final purpose. eVTOL to NYC shows this. We may see quieter, less polluting cheap taxi service, basically a superior ability to function, because of being electric. If you only look for reasons it is worse, you will find them and not progress.