5 ms·
> reduced weight in other parts of an aircraft The bigger problem is that the overall weight increases. Rearranging the COG doesn't really matter when most of
by MegaButts 1y ago
> reduced weight in other parts of an aircraft
The bigger problem is that the overall weight increases. Rearranging the COG doesn't really matter when most of your energy is spent literally fighting gravity.
This is the first thing that popped up in google when I wanted to compare gravimetric density between gasoline and lithium ion batteries. Gasoline is still approximately 30x denser. That is at least one revolutionary breakthrough in battery technology away, if not several.
https://research-archive.org/index.php/rars/preprint/download/388/937/724 https://research-archive.org/index.php/rars/preprint/downloa...
- GaggiX 1y agoConsidering the thermal efficiency of a modern jet engine, the usable energy compared to a lithium battery will be ~15 higher per kg, still bad, but not as bad.
- timschmidt 1y agoAlso some napkin math using common examples gives a range of 0.2 - 1.2 horsepower / kg for gasonline motors, and 8 - 21 horsepower / kg for electric. So even though the batteries weigh more, the motors weigh less.
- numpad0 1y agoDoesn't it compound since it costs fuel to carry fuel in a flying machine? I'm not sure about math but isn't it like 1/15th Isp, even with that maximally optimistic value?
- seb1204 1y agoThis is not correct for electric trucks. Replacing diesel motor and gearbox with battery pack and electric drive train is close to a zero sum game according to https://youtube.com/@electrictrucker?si=RjdWBQQXansebUyJ https://youtube.com/@electrictrucker?si=RjdWBQQXansebUyJ Definitely not a huge penalty.
- dmoy 1y agoFair, but the context here is planes (and boats I guess though that seems less difficult than planes)
- hedora 1y agoContainer boats are ridiculously carbon efficient because they move unimaginable amounts of weight (amortizing any fixed costs like keeping the engine running) slowly (low drag) over a perfectly level surface (no loss from going up hill). Almost any carbon reduction scheme that involves doing anything other than using them doesn’t work. For instance, the embodied carbon of an apple that goes from China to the US, then is driven to a Walmart in a diesel train / semi is probably lower than the carbon footprint of one from the local farmers market (unless the farmer drives the apples to market in an EV and the local power grid is low carbon).
- dmoy 1y agoRight and it's precisely because they can have unimaginable amounts of weight that it's a more tractable thing to solve compared to electric planes. I don't think the article is debating cargo ship vs car carbon footprint here, it's just the feasibility of electric cargo ship vs bunker fuel cargo ship. (And planes, which seems way harder)
- cryptonector 1y agoAirplanes don't get to do regenerative braking except briefly upon landing, but you're not going to put generators in the wheels just for that, and you need active thrust reversers, so really there is simply no room for regenerating power in electric planes.
- perilunar 1y agoThere’s no reason why you couldn’t do regen when descending with an electric-powered prop plane. It would give a steeper descent than normal, and may not be more efficient overall than cutting power earlier and descending more gradually, but it could be done.
- jmward01 1y agoThe point was the other parts of the plane. No lines moving all that gas around and the pumps and the plumbing in and around the engine and the bleed air piping and the and the and the.... There are a lot of potential places to shave weight when you go electric. An aircraft optimized for electric will be massively different if done right.
- cryptonector 1y agoThe way jetliners scale shaving the weight of those things (and note that you're not counting the weight of electric cables that can carry hundreds of amps) is nothing. It might be something for tiny airplanes, but that's it.