The age of electric flight is finally upon us • Hacker News Board

Re: The age of electric flight is finally upon us

#31

Post by Rychard » Fri, Jun 21, 2019, 2:51 PM UTC

j9461701 wrote: post #24

SeanBoocock wrote: post #16

Earlier quoted context omitted.

From the article: > Even assuming huge advances in battery technology, with batteries that are 30 times more efficient and "energy-dense" than they are today, it would only be possible to fly an A320 airliner for a fifth of its range with just half of its payload, says Airbus's chief technology officer Grazia Vittadini. > "Unless there is some radical, yet-to-be invented paradigm shift in energy storage, we are going…

This is why I'm so excited for lithium-air batteries. Theoretically they'd carry ~40.1 MJ/kg, which is very competitive with gasoline's ~46.8 MJ/kg. Factoring in the higher efficiency of electric drives (95% vs. 35% for say a regular ICE car), you'd be getting effectively over double the energy per pound in terms of moving you around.

Burning fuel reduces weight, so the range per unit of (remaining) fuel is greater.

Batteries however, weigh the same amount regardless of charge level.

I wonder if this affects the calculations in an appreciable way.

Re: The age of electric flight is finally upon us

#32

Post by usrusr » Fri, Jun 21, 2019, 2:51 PM UTC

afiori wrote: post #4

wlesieutre wrote: post #3

Earlier quoted context omitted.

To store enough hydrogen to be useful you probably need it in liquid form like rockets use. Hydrogen is energy dense by mass, but not by how much space it takes up compared to liquid fuels. Otherwise you'll have a really giant bag of gaseous hydrogen which does help your bouyancy, but then you've made an airship instead of a plane and a spark accidentally turns it into the Hindenburg.

Is it so much less energy dense per liter to offset the gain in weight? In a plane energy per weight is rather important afterall

The penalty for more volume is rising with higher speed, whereas the penalty for more weight is staying pretty much constant. In a fast plane, volume is just as important as weight, if not more.

Re: The age of electric flight is finally upon us

#33

Post by rootusrootus » Fri, Jun 21, 2019, 2:53 PM UTC

nradov wrote: post #19

ginko wrote: post #2

I'm surprized hydrogen fueled flight isn't looked into more. Hydrogen can be produced using electrolysis and it's packs significantly more energy per weight even than kerosene. The main drawback is the low density which would require larger fuselages, but that should be offset by the significantly lower weight.

Hydrogen is hardly ever produced by electrolysis. It's very inefficient. https://en.wikipedia.org/wiki/Hydrogen_production

But the three alternative methods for production are fossil fuel based. Kinda defeats the point.

Re: The age of electric flight is finally upon us

#34

Post by AtlasBarfed » Fri, Jun 21, 2019, 2:53 PM UTC

ginko wrote: post #2

I'm surprized hydrogen fueled flight isn't looked into more. Hydrogen can be produced using electrolysis and it's packs significantly more energy per weight even than kerosene. The main drawback is the low density which would require larger fuselages, but that should be offset by the significantly lower weight.

Hydrogen production is either not carbon neutral (from ?natural gas?) or isn't particularly efficient to produce once you tack on transport with electrolysis losses.

Re: The age of electric flight is finally upon us

#35

Post by isostatic » Fri, Jun 21, 2019, 2:53 PM UTC

SeanBoocock wrote: post #16

iambateman wrote: post #10

From the article: conventional fuel for a 100 mile flight costs $400, while electric energy would cost $12. This seems like such a tremendous difference that the market would be in an arms race to make it a reality. Especially considering electric motors have fewer moving parts and so require less maintenance. Oh and it would be so quiet.

From the article: > Even assuming huge advances in battery technology, with batteries that are 30 times more efficient and "energy-dense" than they are today, it would only be possible to fly an A320 airliner for a fifth of its range with just half of its payload, says Airbus's chief technology officer Grazia Vittadini. > "Unless there is some radical, yet-to-be invented paradigm shift in energy storage, we are going…

A320 family range varies from 5500km to 8700km, so "a fifth of it's range" is around 1500km, which is 80% of the industry emissions.

I'm not sure of that quote either -- a lithium ion battery is currently about 1MJ/kg and 1MJ/litre. Jet fuel is 43MJ/kg and 35MJ per litre (values from from wikipedia)

So a battery that's 30 times more energy dense will be in the region of jet fuel, and thus would presumably be able to fly an A320 for its current range with its current payload.

To do current payloads at 1/4 range (what you'd need for those flights under 1500km) at A320 payloads, you'd need batteries to presumably be in the 5-10 times as dense level, and that's the range that lithium-air batteries would sit.

Re: The age of electric flight is finally upon us

#36

Post by base698 » Fri, Jun 21, 2019, 2:56 PM UTC

rootusrootus wrote: post #30

NickM wrote: post #17

Earlier quoted context omitted.

Yeah I have wondered about this option as well. Hydrogen fuel cell cars make very little practical sense for a lot of reasons, but most of those reasons don't seem to apply so much when you're dealing with air travel: - It'll be a long time before fuel cells are cost competitive with gas or electric cars, but for planes the cost of fuel and operation is much more significant than with a car, so the upfront cost for b…

> if a plane crashes there's a good chance everyone dies anyway That's actually not the case. Overall your odds of surviving an accident in a plane are something like 95%. Still above 50% for "serious" incidents. Sure, if the plane drills the ground everyone is going to die, but planes crash somewhat regularly with most/all surviving.

To further the above point, here is a searchable database provided by the NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx

Re: The age of electric flight is finally upon us

#37

Post by Yizahi » Fri, Jun 21, 2019, 2:57 PM UTC

Simple electric wheel on aircrafts for taxiing (as compared to the electric powered flight) took almost 10 years from first demo tests and it still hasn't entered production on commercial airlines. And that thing is completely possible with modern tech. I highly doubt we will see electric powered aircrafts (bigger than small* experimental crafts) in our lifetimes. Way too much limitations existing today. But it would be nice if for some reason it will happen sooner.

PS: *small in capacity. I do know that for example Solar Impulse is the biggest aircraft by wingspan.

Re: The age of electric flight is finally upon us

#38

Post by Tade0 » Fri, Jun 21, 2019, 2:59 PM UTC

wlesieutre wrote: post #13

afiori wrote: post #4

Earlier quoted context omitted.

Is it so much less energy dense per liter to offset the gain in weight? In a plane energy per weight is rather important afterall

As a gas at 1 atmosphere, wikipedia says 0.011 MJ/L, compared to jet fuel at 35 MJ/L. You'd save weight (it weighs less than air so this would make you float) but need 3000x as much space if it's not compressed. Compressed at 690 bar (about 680 atmospheres) it goes all the way up to 5 MJ/L, only 7x as much volume of fuel required compared to jet fuel. But the tanks to pressurize something that much are presumably ver…

Counterintuitively enough liquid ammonia packs more hydrogen than liquid hydrogen per unit volume - also it condenses at -33C (-27.4F), so it actually wouldn't require cooling once in the air.

It can be burned in a gas turbine, but for now the NOx emissions are pretty horrible.

Re: The age of electric flight is finally upon us

#39

Post by gambiting » Fri, Jun 21, 2019, 3:00 PM UTC

ginko wrote: post #2

I'm surprized hydrogen fueled flight isn't looked into more. Hydrogen can be produced using electrolysis and it's packs significantly more energy per weight even than kerosene. The main drawback is the low density which would require larger fuselages, but that should be offset by the significantly lower weight.

1kg of kerosone can be kept in a plastic tank that weighs nothing. 1kg of hydrogen has to be kept in a pressurized, pure-lead 70kg bottle, and even then hydrogen will diffuse through it in just few weeks. So to take 1kg of hydrogen with you you're taking a lot of weight in the tanks too.

Re: The age of electric flight is finally upon us

#40

Post by base698 » Fri, Jun 21, 2019, 3:01 PM UTC

taf2 wrote: post #22

I wonder if with electric we can fly higher like much higher maybe 80k to 90k since we don’t have to worry about the engine stalling. Could this also make the flight times comparable or faster? For sure less turbulence. As someone who lives on a flight path I’m eager for the change in noise pollution too- though I’m worried the transition will take decades...

Engines don't stall, planes do. Plane stalls are about aerodynamics, and nothing to do with the engine.

Current engine designs operate poorly at higher altitudes for a number of reasons: less air density meaning less oxygen to burn and less air to push against. Turbine engines can flame out, which maybe that's what you were referring: https://en.m.wikipedia.org/wiki/Flameout