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Comment by lm28469 | Hacker News Reader

> battery technology only needs to equal about 25-30% the raw energy density of fuel

"only" is doing a lot of work here, current lithium batteries are under 1 MJ/kg while good ol car gasoline is at 40+ MJ/kg

top fuel dragsters run nitromethane which is 4 times less energy dense than regular gas yet the go much faster so clearly there is much more going on than just energy density, like the fact that they have to entirely rebuild their engine every other day. I don't even think energy density is a big deal, it's more about how fast you can convert it into movement, and explosions are very good at that type of large scale conversion

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AFAIK the big problem with an electric drag racer is weight/mass. Batteries are heavier than fuel. Electric motors are fantastic at acceleration, but you have to feed them with enough amps to make that happen.

A drag racer doesn't need range, so storing a large volume of energy probably isn't the problem. But having enough batteries to supply enough amperage to get that kind of acceleration is probably adding too much weight to be competitive.

This is also the problem with battery powered aviation. The majority of the energy used in a flight is on takeoff and ascent, effectively lifting all that mass to cruising altitude.

> majority of the energy used in a flight is on takeoff and ascent

That's an exaggeration or a misstatement. Even flying the shortest possible flight (a single takeoff and climb, followed by a descent and landing at a very nearby airport) is overwhelmingly likely to use more total energy in the taxi, cruise, descent, landing, and taxi portions. I looked through some of my datalogs from flights where I flew circuits back to the same airport and the fuel (energy) used for a takeoff and climb to pattern altitude was only rarely more than the fuel used for the rest of the circuit, and that was only when practicing emergency turnbacks from a simulated loss of thrust on takeoff.

The peak power is used on takeoff, but the majority of energy is used in cruise.

> A drag racer doesn't need range

in fact it only needs 1/4 of a mile!

Less. 1,000 ft (vs the 1/4 mi distance of 1,320 ft). They shortened the run in 2008 after the cars had gotten too fast and a crash killed a driver.

Interesting, found an article:

https://www.dailynews.com/2013/11/09/nhra-debate-rages-on-10...

Talks about runoff space at smaller venues, tires, insurance, etc

> rebuild their engine every other day

Top fuel engines are torn down and rebuilt between runs.

superchargers (compressed air), huge sets of staged injectors, low compression ratios, stoichiometric ratio of nitromethane to air (1.7:1 instead of ~14.7:1 like normal petrol!) - as you say, it's about how fast you can convert the liquid to an explosion.

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