Hacker News Reader

Comment by choeger | Hacker News Reader

I don't know. Sure, if you can build batteries with the energy density of gasoline, you can build an electric plane with them. But is this really necessary?

Right now, we have relatively large, relatively fast, jet planes. Do we need that size and that speed to be commercially viable? Could we also run a larger fleet of smaller, more automated planes or helicopters? If there was no kerosene left by tomorrow morning, would there really be no alternative?

View on HN

I probably have a skewed perception because I play with small fpv drones, but any weight saving like this usually opens up a whole world of new possibilities we never bothered to imagine before. This will certainly help existing delivery drones and drone taxi projects.

> If there was no kerosene left by tomorrow morning

I suspect the medium term solution would be to make some, either from other hydrocarbons or plant cellulose, or even by the US Navy seawater CO2 to liquid fuel process.

> I don't know. Sure, if you can build batteries with the energy density of gasoline, you can build an electric plane with them. But is this really necessary?

Only if you value overseas travel... It currently takes ~16 hours to fly from SF to Singapore depending on weather. Any longer, and you're going to see a lot of that travel disappear.

Only if you value overseas travel... It currently takes ~16 hours to fly from SF to Singapore depending on weather. Any longer, and you're going to see a lot of that travel disappear.

It takes that long because it's more efficient to do it in a single flight. Taking off and landing are a massive waste of time and fuel. If we only had short range planes people would change their destinations in some cases or they'd plan layovers as part of the trip. I don't think you'd see that many people just stop travelling abroad.

Indeed. Though like in the olden days the large number of stopovers might cut down demand somewhat:

https://en.wikipedia.org/wiki/Kangaroo_Route#Multiple_stops

In the era when planes had to do that, there was not much trans-oceanic travel. The Pan Am flying boats, the "China Clippers", went from San Francisco to Hawaii to Midway to Wake to Guam to Manila to Macao to Hong Kong. It took a week.[1]

[1] https://tripsintohistory.com/wp-content/uploads/2012/10/Clip...

it's not really true that ultra long range direct flights (eg. from sfo to sin) are more efficient.

the efficiency gain by not taking off and landing is eaten away by the efficiency loss of having to carry so much fuel (which also comes at the expense of useful load..)

It's not difficult to imagine in-flight recharging from something like a KC-135 running a big fat generator. If you're recharging capacitors, connect time would probably be a minute or two.

I'm not so sure about that being an acceptable solution for civilian transportation… Even assuming automation can eliminate the risks and training overhead associated with in-flight refueling, there are still be some major hurdles that would need to be addressed before this could be considered a viable solution. The 3 big ones that come to mind are:

What happens if the KC-135 misses the rendezvous? What if the charging port fails to work for some reason? What about the carbon footprint of these airborne generators?

Plus, now you have the weight of the capacitors to carry around all the time, further reducing the effective payload.

> What happens if the KC-135 misses the rendezvous? What if the charging port fails to work for some reason?

The same thing that happens today with combustion aircraft: the crew makes an emergency landing if they can, or bails out and waits for a Seahawk to pick them up.

This actually happens with fuel-driven aircraft regularly today.

Bailing out seems a bit problematic for passenger aircraft.

I kinda enjoy the ability to get to the other side of the world in 24 hours.

> if you can build batteries with the energy density of gasoline

Actually significantly worse than that. A plane gets lighter the longer it flies, especially at takeoff when everything is at max thrust. A battery becomes more and more dead weight the longer you fly.

I wonder if this could be solved for with detachable take-off booster. Gets you up in the air, then returns to the airport.

Couldn't you just start with a cable that detaches and is pulled back to the landing strip?

Just make sure it detaches properly, you don't wanta a dozen wire to yank you in mid ascend

A "third rail" along the runway and a dodgem/Scalextric type conductor springs to mind.

I keep seeing numbers around 500 miles range floated for 8-12 passenger electric aircraft.

Fire up google earth and start drawing 500 mile radius circles around metro areas.

You probably don’t need gasoline density equivalents for short haul flights, but we’re still really far off from where we need to be.

the problem with jets is stratospheric water vapor in addition to all the CO2 they emit (quite a lot in itself).

Reply on news.ycombinator.com